Moving bottom incinerator

ABSTRACT

A moving bottom type incineration oven having: an inlet for supplying mineral pebbles or grains, the inlet being located in a first side wall of the oven; an outlet for removing the incinerated residue and the mineral pebbles or grains, the outlet being located in a second side wall of the oven, opposite the first side wall; and a conveying means forming the bottom of the oven and having an upper surface running from the inlet toward the outlet. Mineral pebbles are deposited on the upper surface of the conveying means to form a layer thereon. Rubbish deposited on the layer of mineral pebbles is incinerated. The conveying means may be a single conveyor or a combination or plurality of conveyors of relatively short length arranged as stairs. The combustion gas may be introduced into the oven through the layer of mineral pebbles or crushed rock, or alternatively, through port or ports in the side walls.

United States Patent [191 Saitoh et al.

[ Jan. 21, 1975 MOVING BOTTOM INCINERATOR [73] Assignee: Kureha KagakuKogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: July 20, 1973 [21]Appl. No.: 381,356

Primary Examinerl(enneth W, Sprague [57] ABSTRACT A moving bottom typeincineration oven having: an inlet for supplying mineral pebbles orgrains, the inlet being located in a first side wall of the oven; anoutlet for removing the incinerated residue and the mineral pebbles orgrains, the outlet being located in a second side wall of the oven,opposite the first side wall; and a conveying means forming the bottomof the oven and having an upper surface running from the inlet to wardthe outlet. Mineral pebbles are deposited on the upper surface of theconveying means to form a layer thereon. Rubbish deposited on the layerof mineral pebbles is incinerated. The conveying means may be a singleconveyor or a combination or plurality of conveyors of relatively shortlength arranged as stairs. The combustion gas may be introduced into theoven through the layer of mineral pebbles or crushed rock, oralternatively, through port or ports in the side walls.

11 Claims, 5 Drawing Figures PATENTED JANZI I975 FIG.

MOVING BOTTOM INCINERATOR BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a rubbish incineration oven having amoving bottom, and more particularly to a rubbish incineration ovenhaving a conveyor forming a bottom in the oven and extending from aninlet for introducing mineral pebbles or grains to an outlet throughwhich the incinerated rubbish and the pebbles are removed. The upper runof the conveyor is adapted to carry a layer of mineral pebbles.

2. Description of the Prior Art The nature of municipal solid waste haschanged with recent advances in container and packaging technology and agenerally rising level of affluence. The recent tendency is that thetype rubbish containing a high amount of moisture has decreased inquantity, while plastic waste has increased. The conventionalincineration oven is designed for incinerating rubbish having arelatively low calorific value. Thus such a conventional oven will havea short service life when used to incinerate plastic wastes which havevery high calorific values and which generated corrosive gases. For thisreason, the conventional type incineration oven is suitable for theincineration of plastic rubbish or waste. Thus, there exists a need inthe art for an incineration oven adapted to incinerate plastic rubbishor rubbish containing large amounts of plastic waste.

The incineration of plastic waste or rubbish requires a great amount ofair. The production of soot results from poor circulation of air flowwithin the incineration or from inadequate air, which conditions resultin incomplete combustion. In addition, the metallic fire lattice whichsupports the rubbish during combustion is subject to corrosion due toHCl, S S0 HCN, N0 etc. contained in the exhaust gas. Furthermore, tarmatter from the rubbish tends to clog the openings of the fire lattice.

SUMMARY OF THE INVENTION It has now been found that the foregoing andrelated disadvantages are overcome by a moving bottom type incinerationoven having: an inlet for supplying mineral pebbles or grains, the inletbeing located in a first side wall of the oven; an outlet for removingthe incinerated residue and the mineral pebbles or grains, the outletbeing located in a second side wall of the oven, opposite the first sidewall; and a conveying means forming the bottom of the oven and having anupper surface running from the inlet toward the outlet. Mineral pebblesare deposited on the upper surface of the conveyor means to form a layerthereon. Rubbish deposited on the layer of pebbles is incinerated. Thepebble layer protects the conveyor from corrosive combustion gaseshaving high calorific value and allows continuous incinerator operation.

In one embodiment of the invention, there is provided a moving bottomtype incineration oven which has a plurality of conveyors of relativelyshort length which are arranged so as to form stairs, thereby increasingthe mixing of the rubbish by turnover at the junctions of the conveyors.

At least part of the combustion air may be introduced through the layerof the mineral pebbles or grains. Alternatively, the combustion air maybe introduced through a port or ports in the side walls.

Accordingly, it is a principal object of the invention to provide anincineration oven which solves the metal lattice corrosion problem andwhich permits continuous operation. 4

Other objects and further scope of applicability of the presentinvention would become apparent from the detailed description to follow,taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional diagram ofa moving bottom type incineration oven of the present invention;

FIG. 2 is a cross-sectional diagram of another embodiment of the movingbottom type incineration oven of the present invention;

FIG. 3 is a cross-sectional diagram of a yet another embodiment of themoving bottom type incineration oven of the present invention havingstepped conveyor means; and

FIGS. 4 (a) and 4 (b) are perspective views of fire lattices suitablefor use in the incineration oven of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an incinerator ofthe present invention having an inlet 1 for the introduction of rawwaste and an inlet 2 for supplying pebbles or crushed stones to form alayer on conveyor 3 which covers the bottom of the oven. Shown at 4 is amain burner, at 5 a subsidiary burner and at 7 an inlet through whichthe combustion air is supplied to the interior of the furnace. Sealingmeans 10 seals the lower portion of the oven. A blower 11 is providedfor introducing combustion air. A screen 12 serves to separate themineral pebbles or crushed rock from the ashy residue.

The conveyor 3 which forms a moving bottom for the oven may be aperforated endless strip capable of withstanding the elevatedtemperature, as shown in FIG. 1, or in the form of a plurality ofscrapers 14 which move along a stationary perforated plate 13, as shownin FIG. 2.

The perforated endless strip may be the type shown in FIG. 4 (a), i.e.,a metal lattice or the type shown in FIG. 4 (b), i.e., a run of aplurality of metal strips coupled to each other. In operation a supportmaterial, mineral pebbles or grains of a relatively large size, arecontinuously supplied to the endless perforated metal strip so as toform a layer 9 having a depth y within the range of from 5 to cm, thusforming an oven bottom 8. The raw waste or rubbish is continuously fedthrough the inlet 1 onto the oven bottom 8 for the incineration by meansof the main burner 4. The main burner is used only in the initial stageof the incineration, and thereafter the combustion is self-sustainingdue to the heat of the burning rubbish, thus obviating the use of themain burner as a heat source. The combustion air may be supplied throughthe oven bottom 8, i.e., through the layer of the mineral pebbles orgrains, or, alternatively, through port or ports 6 in the side wall ofthe combustion chamber.

The conveyor 3 is operated continuously or intermittently, as required.The speed of the conveyor is controlled to provide a dwell time for therubbish within the oven that will give complete combustion. Thus, whenthe rubbish on the conveyor reaches the discharge end of the oven, therubbish at that point will be completely burned. The ash is dischargedat along with the mineral pebbles or grains. Thus, there is nopossibility of non-combustible matter or combustion residue, i.e. ash,accumulating within the oven. As in FIG. 1, the combustion residue onthe mineral pebbles or grains 2 exits from the oven at outlet 20. Inorder to close off the oven from the outside at that point, adjacent tooutlet 20 is an inlet 21 through which mineral pebbles or grains 2' arecontinuously deposited on the combustion residue. This promotes anincrease in the amount of air entering the oven through its bottomportron.

The mineral pebbles or grains 2' to be used at the outlet 20 may be thesame as those (indicated at 2) employed at the inlet. The mineralpebbles or grains coming off of the end of the conveyor 3 are separatedfrom the combustion residue by means of a screen 12, and recycled byreturning a part thereof to the inlet for mineral pebbles or grains 2,and the remainder to the inlet 21.

The conveyor 3 may be an endless strip of a plurality of metal plates,bars or lattice elements coupled to each other. If required, acombination of such conveyors may be used. With a combination orplurality of conveyors, the conveyors are arranged so as to form stairsor steps, as shown in FIG. 3. Thus, when the rubbish is transferred fromone conveyor to another, a mixing action or agitation results, thusimproving the combustion efficiency. The lengths of the conveyors asused in such an embodiment are not necessarily the same, i.e., thelength of the first conveyor may be longer than that of the following,depending on design requirements.

Each individual metallic conveyor may be provided with air ports 15 asshown in FIG. 3 to introduce air through the layer of mineral pebbles orgrains from below; or stationary air injecting tubes may be providedadjacent the upper or lower flight of the conveyor for supplying thecombustion air. Air injection nozzles are provided along the air supplytube 15. The air injection nozzles are directed upwardly where thesupply tubes 15 are below the upper flight or run of the conveyor, andare directed downwardly where the air supply tubes 15 are above theupper run of the conveyor.

If the metallic conveyor has perforations such as 16 (FIG. 4a) or 17(FIG. 4b), air will freely flow into the oven because of the negativepressure existing within the oven, and thus no air feeding device isnecessary. However, in cases where a great amount of air is required asin the case of the combustion of the plastic waste, means for forcefeeding air into the oven is required. The flow rate of the air enteringmay be easily regulated. It should be noted, however, that the lowerportion of the oven may be sealed airtight to force the air into theoven through the layer of the mineral pebbles or grains. However, thecombustion air need not necessarily be supplied through the layer ofmineral pebbles or crushed rock. Part or all of the combustion air maybe supplied through other portions of the oven bottom and/or side walls,but at least part of the combustion air should preferably be suppliedfrom beneath the layer of pebbles.

The layer of the pebbles or grains should be from about 5 to about 100cm in depth. The surface portion of the pebble layer is heated by thecombustion of the rubbish while the lower portion of the layer is at alower temperature, cooled by the air supplied from beneath the layer. Ifrequired, the pebble layer may be made so deep that the melt oftheplastic waste will not reach the conveyor due to the melt becomingsolidified within the pebble layer. The molten plastic generally remainson the surface of the pebble layer. and thus undergoes completecombustion. It should be apparent that the metallic surface of theconveyor will not encounter corrosive gas because of the air passingthrough the layer of the pebbles and because of the negative pressureprevailing inside the oven.

It is preferred that the mineral pebbles or fragments be of such a sizewhich will provide ample void space within the layer so as to permit thefree passage of air therethrough. The pebbles etc. may be any materialof a nature which can withstand the elevated temperature. Quartz pebblescommonly found in alluvial deposits are suitable. Crushed granite, etc.,is also satisfactory.

As is apparent from the foregoing description, the moving bottomincinerator of the present invention, formed of non-combustiblematerials, e.g. crushed rock or pebbles, is well suited for theincineration of plastic waste having a high calorific value and whichgenerates corrosive gas. Another advantage is, by means of the movingbottom, the combustion residue is continuously removed, and the speed ofthe conveyor may be adjusted in accordance with the type of rubbish tobe incinerated. The apparatus of the present invention is ideally suitedfor the incineration of municipal rubbish and like materials.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

We claim:

1. An incineration furnace comprising:

a housing;

means constituting a movable bottom portion of said housing;

means for depositing a support material selected from pebbles andcrushed rock onto said movable bottom portion to form a layer thereon;

means for moving said bottom portion and said layer of support materialtransversely along said housing into a rubbish or waste combustion stageand through an outlet in said housing; means for introducing rubbish orwaste onto the top of said layer prior to said combustion stage;

means for burning said rubbish or waste within said housing to producean incombustible residue; and

means for closing off space above said layer at said outlet so as toobstruct air from entering the housing through said outlet whilepermitting withdrawal of said support material together with saidincombustible residue therefrom.

2. The furnace of claim 1 additionally comprising means for separatingsaid support material from said residue.

3. The furnace of claim 1 wherein said means for moving said supportmaterial along the bottom of the furnace comprises at least one endlessbelt having an upper run and a lower run.

4. The furnace of claim 1 wherein said means for moving said supportmaterial along the bottom of the is in the form of a plurality of metalstrips coupled to 1 each other.

7. The furnace of claim 1 wheren the bottom of the furnace is astationary metal support.

8. The furnace of claim 7 wherein said metal support has a plurality ofaperatures and wherein the furnace additionally comprises means tointroduce combustion air upwardly through said aperatures.

9. A process for the incineration of rubbish or waste in a furnacecomprising:

forming a layer of an incombustible support material selected frompebbles and crushed rock on a bottom portion of the furnace;

moving said layer through the furnace at a predetermined rate;

supplying the rubbish to be burned to the surface of said layer; and

burning said rubbish within the furnace.

10. The process of claim 9 additionally comprising introducing at leasta portion of the combustion air into the furnace upwardly through saidlayer.

11. The process of claim 9 wherein said moving is intermittent.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 861,331 Dated January 21 1975 Inventor(s) Shiqeru Saitoh et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 4 after "oven. the following was omitted:

If necessary to achieve complete combustion, a second or thirdcombustion chamber having subsidiary burners may be provided in series.-

I Signed and sealed this 6th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks USCOMM-DC 60S76-P69 FORM PO-IOSO (10-69) u.s. Govnnunn'nmmms omc: nu o-us-au.

1. An incineration furnace comprising: a housing; means constituting amovable bottom portion of said housing; means for depositing a supportmaterial selected from pebbles and crushed rock onto said movable bottomportion to form a layer thereon; means for moving said bottom portionand said layer of support material transversely along said housing intoa rubbish or waste combustion stage and through an outlet in saidhousing; means for introducing rubbish or waste onto the top of saidlayer prior to said combustion stage; means for burning said rubbish orwaste within said housing to produce an incombustible residue; and meansfor closing off space above said layer at said outlet so as to obstructair from entering the housing through said outlet while permittingwithdrawal of said support material together with said incombustibleresidue therefrom.
 2. The furnace of claim 1 additionally comprisingmeans for separating said support material from said residue.
 3. Thefurnace of claim 1 wherein said means for moving said support materialalong the bottom of the furnace comprises at least one endless belthaving an upper run and a lower run.
 4. The furnace of claim 1 whereinsaid means for moving said support material along the bottom of thefurnace comprises a plurality of endless belts arranged in steppedfashion so that the waste or rubbish is sequentially transferred from anupper endless belt to the next adjacent lower endless belt.
 5. Thefurnace of claim 3 wherein said endless belt has a plurality ofaperatures and wherein said furnace additionally comprises means forintroducing combustion air through said aperatures.
 6. The furnace ofclaim 5 wherein said endless belt is in the form of a plurality of metalstrips coupled to each other.
 7. The furnace of claim 1 wheren thebottom of the furnace is a stationary metal support.
 8. The furnace ofclaim 7 wherein said metal support has a plurality of aperatures andwherein the furnace additionally comprises means to introduce combustionair upwardly through said aperatures.
 9. A process for the incinerationof rubbish or waste in a furnace comprising: forming a layer of anincombustible support material selected from pebbles and crushed rock ona bottom portion of the furnace; moving said layer through the furnaceat a predetermined rate; supplying the rubbish to be burned to thesurface of said layer; and burning said rubbish within the furnace. 10.The process of claim 9 additionally comprising introducing at least aportion of the combustion air into the furnace upwardly through saidlayer.
 11. The process of claim 9 wherein said moving is intermittent.